CVE-2026-20243: Cisco ClamAV out-of-bounds write in ALZ file format parser

CVE-2026-20243 · Severity: high · CVSS 7.5 · Published 2026-07-01

A vulnerability in the ClamAV antivirus engine, which is used to scan files for threats, could allow an attacker to crash the scanning service. By sending a specially crafted ALZ archive file to a system protected by ClamAV, an attacker can cause the software to stop functioning, potentially leaving the system unprotected or requiring a manual reboot. On Windows systems, this is particularly serious as the scanning process runs with high privileges and its failure can impact overall system stability.

Technologies: Cisco ClamAV, Cisco Secure Endpoint Connector for Linux, Cisco Secure Endpoint Connector for Mac, Cisco Secure Endpoint Connector for Windows. Vendors: Cisco.

Quick answers

Is CVE-2026-20243 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-20243 being exploited in the wild.
How severe is CVE-2026-20243?
High severity, with a CVSS score of 7.5, published 1 July 2026.
Which products and versions are affected?
Cisco Secure Endpoint Connector for Linux Prior to 1.29.0; Cisco Secure Endpoint Connector for Mac Prior to 1.27.2; Cisco Secure Endpoint Connector for Windows Prior to 8.6.2.
Is there a fix for CVE-2026-20243?
No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-20243 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-20243?
Check whether you run Cisco ClamAV, Cisco Secure Endpoint Connector for Linux, Cisco Secure Endpoint Connector for Mac or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

A vulnerability exists in the ALZ file format parser of ClamAV due to improper boundary checks during file scanning. This flaw leads to an out-of-bounds buffer write (CWE-120) when processing specially crafted ALZ content. An unauthenticated remote attacker can exploit this by submitting a malicious file for scanning, causing the ClamAV process to terminate. While primarily a Denial of Service (DoS) issue, memory corruption could potentially lead to other impacts, though Cisco notes that modern memory protections make remote code execution difficult. The impact is highest on Windows platforms where the process runs in a privileged context. Fixes have been released for ClamAV and integrated Cisco products like Secure Endpoint.

Affected products

  • Cisco ClamAV
  • Cisco Secure Endpoint Connector for Windows Prior to 8.6.2
  • Cisco Secure Endpoint Connector for Linux Prior to 1.29.0
  • Cisco Secure Endpoint Connector for Mac Prior to 1.27.2

Timeline

  • 2026-07-01: advisory: Cisco and NVD published the advisory.

References

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